Senegal (sĕnĭgôlˈ, sĕnˈĭgôl) [key], river, c.1,000 mi (1,610 km) long, formed in SW Mali, W Africa, by the confluence of the Bafing and Bakoy rivers, both of which rise in the Fouta Djallon, N Guinea. The river flows north, then generally west to form the Mauritania-Senegal border before entering the Atlantic Ocean at St.-Louis, Senegal. The Falémé River, which forms the Senegal-Mali border, is its chief tributary. Entrance to the river from the sea is impeded by sandbars and a complex delta region. The river is tidal c.300 mi (480 km) upstream, and during the rainy season it is navigable to Kayes, Mali. The river is an important source of irrigation water; rice is grown on the floodplain. In 1968, Guinea, Mali, Mauritania, and Senegal established the Organization of Senegal River States to develop the Senegal valley. It was succeeded in 1972 by the Organization for the Development of the Senegal River Valley (OMVS), of which Guinea is not a member.